http://en.wikipedia.org/wiki/Gilding

The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to wood, stone or other surface to give a thin coating of gold. A gilded object is described as "gilt".  Methods of gilding include hand application and glueing. Parcel-gilt (partial gilt) objects are only gilded over part of their surfaces. This may mean that all of the inside, and none of the outside, of a chalice or similar vessel is gilded, or that patterns or images are made up by using a combination of gilt and un-gilt areas.

Mechanical gilding includes all the operations in which gold leaf is prepared, and the processes to mechanically attach the gold onto surfaces. The techniques include burnishing, water gilding and oil-gilding used by wood carvers and gilders; and the gilding operations of the house decorator, sign painter, bookbinder, the paperstainer and several others.

"Overlaying" or folding or hammering on gold foil or gold leaf is the simplest and most ancient method.

If gilding on canvas or on wood, the surface was often first coated with gesso. "Gesso" is a substance made of finely ground gypsum or chalk mixed with glue. Once the coating of gesso had been applied, allowed to dry, and smoothed, it was re-wet with a sizing made of rabbit-skin glue and water ("water gilding", which allows the surface to be subsequently burnished to a mirror-like finish) or boiled linseed oil mixed with litharge ("oil gilding", which does not) and the gold leaf was layered on and left to dry. 

Other gilding processes involved using the gold as pigment in paint: the artist ground the gold into a fine powder and mixed it with a binder. Then the gold was applied in the same way as with any paint. Sometimes, after either gold-leafing or gold-painting, the artist would heat the piece enough to melt the gold slightly, ensuring an even coat. These techniques remained the only alternative for materials like wood, leather, and the vellum pages of illuminated manuscripts.

The ancient art of gilding can add a touch of class to custom projects.

By Mac Simmons
http://www.woodweb.com/knowledge_base/A_Little_About_Applying_Gold_Leaf.html

Gold leafing is an art that dates back to at least 2500 BC. This ancient decorative art began when a tiny piece of malleable precious metal was beaten down into a delicately fine sheet of gold, with a thinness of only 4 to 5 millionths of an inch. These fragile sheets of gold were overlaid onto an object, an art which became known as "gilding."

Gilding can add an extra decorative touch to custom woodwork and may be useful in doing certain types of antique reproductions. This article is intended to help you get started in the art of gold (and silver) leafing. Although this is just an introduction, it will acquaint you with the basic methods and give you some tips to begin.

Gold and silver leafing can be done on almost any clean substrate, including wood, leather, metal, plastic or glass. The materials needed can be purchased from most finishing suppliers or arts and crafts supply stores. The leaf generally is sold in books. 

The process starts with gold size, which is a type of varnish that is sold in slow or fast drying types. Polyurethane or varnish can also be used as sizing. The sizing is what the gold leaf adheres to while it is drying and is applied with a flat brush. Once the sizing has dried, the leaf is permanently held in place.

The gold leaf will only adhere where the sizing is applied, so you must be careful to apply the sizing to the desired area completely. On the other hand, if you accidentally touch a spot with sizing that you don't want gilded, the sizing should be wiped off with mineral spirits, or gold leaf will stick to the unwanted area. (Brushes also should be cleaned in mineral spirits as soon as you are finished using them.)

After sizing is brushed on, allow it to set up until it becomes tacky. It must be tacky but not totally set-up, or the leaf will not stick to it. Once the size feels tacky to the touch, the gold leafing process can begin.

For your initial gilding attempts, I suggest you start out using the less expensive Dutch metal composition leafing rather than pure gold or silver leaf until you have perfected the application technique. It is extremely important that wherever you do your leafing, there are no wind, drafts, air circulation or other people walking around the room, as the gold leaf is very lightweight, and any air movement will disturb it, making it very difficult to lay onto the work.

To apply the leaf, pick up a sheet by the corners and gently lay it in place, with each sheet slightly overlapping the previous one. (Tip: First rub your fingers through your hair or on your pants to pick up some static electricity, which makes it easier to pick up the sheets of leaf.)

Any leaf that rips or falls off should be saved. These pieces can be used to fill in any areas where the leaf does not stick or that you have missed. When applying leaf on scrolled edges, carvings, turnings or mouldings, a brush is used to lightly push it into the crevices. (This is often where the leaf may break and leftover pieces can be reused.)

Depending on the size of the area to be gilded, you may want to cut the leaf before laying it over the work. While it is still in the book, you can use an Exacto knife, a pair of sharp scissors or a single-edge razor blade to cut the leaf. Cut it a little larger than the area you will be gilding. This makes it easier to work and ultimately will save a lot of wasted leaf.

A gentle touch is recommended for applying gold leaf. It should just be placed over the tacky sizing and then released to fall on it. If necessary, you can use a brush to lightly push the leaf down flat. After you have laid down the sheets of leaf and covered the entire surface, if you missed any spots you can apply a little size, allow it to get tacky and place a small leaf onto it. A flat brush can be used to lightly tap down the patch. These repairs should blend in with the entire leafing. Then allow the sized leaf to thoroughly dry overnight.

After the sized leaf has dried, take a 1-, 2- or 3-inch flat brush and work it lightly back and forth, softly fanning against the leafing. This will remove all of the excess overlapped leaf that did not stick to the sizing. If any of the gold leaf sticks to the brush, it means the sizing is not thoroughly dry and you should allow more dying time. The drying time depends on many variables, including the type of sizing you use, the substrate and the temperature in your shop. After working with it, you will get to know how long the dry time is for your sizing and your shop. The longer you can allow it to dry, the fewer problems you will have.

After the gilding is complete, you can apply a coating. Shellac, varnish, polyurethane or lacquer will add an amber color to the leaf. If you want a water-clear coating, use a clear shellac or a water-clear acrylic lacquer, which is a crystal-clear, non-yellowing coating.

To obtain various special effects, you can use different colored primers, antiquing colored glazes or polishing agates to burnish the leaf. You also can add some fly specks and distressing marks or scratch and sand through the leaf to allow color primers to show through, to create an aging process in the gold leaf.

For your first attempts, you can try leafing on small parts. Once you get the touch, you can leaf anywhere you want to add some gold and silver effects. With a little imagination, you can even combine gold and silver together to achieve many different looks. Gilding can add a touch of class to your work, enhancing and enriching it with a look that only gold and silver leaf can achieve.